INSERT
INTO C1_ROLE_PERMISSION
  (
    ROLE_ID,
    PERMISSION_ID
  )
  (SELECT :roleId,
      :permissionId
    FROM dual
    WHERE NOT EXISTS
      (SELECT 1
      FROM C1_ROLE_PERMISSION e
      WHERE e.role_id     = :roleId
      AND e.PERMISSION_ID = :permissionId
      )
  )